1. Field of the Invention
The present invention relates to an automatic full-web stretch-wrapping apparatus designed to wrap a load in a stretchable film, and in particular, it relates to an automatic full-web stretch-wrapping apparatus which includes a turntable to rotate a load thereon and a gripper arranged on the turntable for gripping the leading end of a film whereby the load is wound with one turn of stretchable film under tension.
2. Description of the Related Art
A known automatic stretch-wrapping apparatus includes a turntable having a conveyor for transferring a load to and from the apparatus to carry out all steps of winding or wrapping the load on the turntable by a stretchable film under tension while the turntable is rotated. There are two types of automatic stretch-wrapping apparatuses; one type is called a spiral winding type in which a narrow film is spirally wound around a load in a plurality of turns, as disclosed, for example, in Japanese Unexamined Utility Model Publication (Kokai) No. 57-95302; and the other type is called a full-web type in which a wide film having a width substantially equal to or greater than a height of a load to be wrapped so that the load is fully wrapped between the upper and lower edges of the film, as disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 53-11690.
Either of these two types includes a gripper for gripping the leading end of a stretchable film supplied from a roll, which gripper is mounted on the turntable at the side surface thereof so that the gripper can take, gripping position in which the gripping fingers of the gripper project above the upper surface of the turntable and grip the film and a releasing position in which the gripping fingers of the gripper retract below the upper surface of the turntable and release the film. The gripper is in the gripping position at the initial stage of the operation, and the turntable with the load is rotated by a certain angles greater than 360 degrees to wrap the load by the film so that the film is wound around the load in one plus a little more turns so that the second partial turn of the film overlaps the first turn of the film whereby the first turn of the film is fastened to the load by the second turn of the film. The gripper is then brought into the releasing position. The turntable is continuously rotated to wrap the load with a plurality of turns of the film. When the turntable is stopped, the gripper is again brought into the gripping position, and finally, the film of cling type is adhered to the load and cut between the load and the gripper, with the next leading portion of the film gripped by the gripper.
A problem arises in the prior art that the first turn of the film around the load is not stretched to function as a stretch-wrapping film because the leading end of the stretchable film (gripped by the gripper) is not securely fixed (e.g. by heatsealing) onto a portion of the film wrapped thereon and it is necessary to wind the film around the load in a plurality of turns. Therefore, the leading portion of the film is wasted even in the full-web type stretch-wrapping apparatus in the prior art.
Also, there is a pass through type stretch-wrapping apparatus, as disclosed in, for example, U.S. Pat. No. 4,413,463, which uses a wide film having a width greater than a height of a load to be wrapped so that the load is wound and tightened by one turn of the stretched film.
However, in this pass through type stretch-wrapping apparatus too, since the wrapping operation is carried out while the load is moving and it is not possible to arrange a so-called "top platen" which can be arranged in the above described stretch-wrapping apparatus having the turntable, there is a problem that a resistance of the stretched film may partially shift a light and high load, for example, comprising empty PET bottles stacked in a plurality of layers, deform its posture or disarrange the alignment of such palletized articles in the process of the load passing through the machine, i.e., in the stretch-wrapping step, although there may be a difference depending on the tensioning system imparting tension to the stretched film.
In addition, if the pass through type stretch-wrapping apparatus is to be used in place of the conventionally used stretch-wrapping apparatus having the turntable, it is necessary to change the layout of the entire automatic wrapping line due to the difference of the dimensions of the stretch-wrapping apparatuses, and an extra investment in installation will be necessary.